Polarization bearing detection type two-dimensional light reception timing detecting device and surface shape measuring device using it

ABSTRACT

A polarization bearing detection type two-dimensional light reception timing detecting device for implementing a fast surface shape measurement that can accommodate an animal body measurement, and a surface shape measuring device using it. The polarization bearing of a detection light is turned in synchronization with slit light scanning, and the polarization bearing is two-dimensionally recorded by two sets of analyzers and storage type image detectors in a crossed Nicols arrangement, and thereby it is possible to determine, with only one-time imaging, timing at which a slit light is beamed into respected pixels in the storage type image detectors.

TECHNICAL FIELD

[0001] The present invention relates to an optical device mainly used tomeasure surface form of an object.

BACKGROUND ART

[0002] Many technologies which measure the surface form of an objecthave been proposed. They are roughly divided into two types: one typemeasures one point at a time and the other type measures many pointssimultaneously. Although the one point measurement type is highlyaccurate and reliable, a large amount of measurement time, from severaltens of minutes to several hours, is needed when measuring a wholeobject surface. On the other hand, while the many point simultaneousmeasurement type has a feature of high-speed, it has difficulties inrespect to reliability and accuracy. A light section method, gratingprojection phase shifting method, and measuring method using confocalmicroscopy (hereinafter referred to as “confocal method”), all of whichare many point simultaneous measurement types, have high reliabilitycompared with other many point simultaneous measurement methods thathave been proposed at the laboratory level and have already been usedpractically. Although these methods are high in speed compared to theone-point measurement type methods, it cannot be said that these aresufficiently high in speed for in-line inspection in the FA field.

[0003] As will be explained later in detail, the light section method,the grating projection phase shifting method, and the confocal methodneed an imaging device as a detector, and some type of scanning whichrequires time. Usually, images are acquired with the imaging device forevery partial scanning. After many repetitions of this process, themeasurement is completed. In practice, one measurement (of one field ofview) involves several tens to several hundreds of images either by thelight section method or the confocal method. A long measurement time isunavoidable since an imaging cycle of a TV camera as an imaging deviceis about 30 images per second. The grating projection phase shiftingmethod, although relatively high in speed, needs at least three imageswhich are captured at the different time, therefore measurement ofmoving objects is still impossible. The light section method, thegrating projection phase shifting method, and the confocal method aredescribed below in detail.

[0004]FIG. 11 is an example of the measurement system proposed on thebasis of the light section method. This system is highly reliable withmany practical applications as indicated in the non-patent reference 1.The figure here shows only one slit light scanning part on a side inorder to explain only the main points of the above-mentioned reference,while the slit light scanning parts are on both the right and left sidesin the reference.

[0005] Images are continuously input to the image processing device 115by a television camera 114, while light from a laser slit light source111, scanned by a scanning mechanism 112, irradiates an object 10 froman angle different from the optical axis of the imaging lens 113. In oneimage as shown on the display device 116 of FIG. 11, one slit willappear distorted according to any irregularities on the surface of theobject 10. While in FIG. 11 the slit light moves from the right to theleft until a slit scan is completed, images of 256 sheets to 512 sheetsare input. For every pixel of the image input, the image processingdevice 115 detects the timing (for example, tp in the figure) at whichthe value of the pixel becomes the largest, that is, when the slit lightpasses over the position on the object 10 with which the pixelcorresponds, and calculates the three-dimensional position of the object10 surface as intersection P between the projection angle of the slitlight at that time and the angle of the main beam of the imaging lens113 determined by the position of each pixel. (Uesugi Mitsuaki, 1993,The Optical Three-Dimensional Measurement edited by Toru Yoshizawa,Shin-Gijyutu Communications, page 39-52)

[0006]FIG. 12 is an example of a measurement system which uses theconfocal imaging system 121. As the confocal imaging system 121, any oneof a laser scanning microscope, Nipkow board scanning microscope,non-scanning confocal imaging system or the like can be used, and thefigure is simplified since any one of these is sufficient.

[0007] The main feature of the confocal imaging system 121 is that onlythe position 122, which is in focus, is imaged, i.e., hardly any lightfrom the portion which is out of focus will reach a detector 123. Thefeature is called optical sectioning. When the image is continuouslyinput using the detector 123 while moving an object 10 in the opticalaxis direction by a Z stage 124, only the in focus portion in the fieldof view is imaged as shown in the display device 116 of FIG. 12 and thisportion expresses the contour line. While the object being moveddownward from top to bottom in the figure until a scan of the Z stage124 is completed, about several hundreds of images are input. The imageprocessing device 115 will detect the timing for each pixel when thevalue of the pixel becomes maximum. That is, the optical system focuseson the position of the object 10 with which the pixel corresponds, andthe position of the Z stage 124 at that time will itself express therelative height of the surface of the object 10.

[0008] Next, the grating projection phase shifting method is brieflyexplained using FIG. 13. The grating projecting method projects aplurality of slit light rays simultaneously on an object while the lightsection method projects one slit light ray. A so-called sinusoidalgrating 132 of the phase shifting method, which will be explained below,is used to make transmittance changes in a sinusoidal curve as shown inFIG. 14. The image of the sinusoidal grating 132 illuminated by alighting source 131 is projected onto the surface of an object 10 by theprojection lens 133, and is imaged by an imaging lens 113 and atelevision camera 114 from a different angle. If the phase of thegrating pattern projected for each pixel of the obtained image is known,the relative relief of the surface of the object 10 can be obtained. Thephase can be determined by the phase shifting method. By shifting thesinusoidal grating 132 by a known value at least twice with the phaseshifter 134, at least three images of the projected grating withdifferent phases are taken. More than three values will be obtained forevery pixel from at least three or more images with different phases,and since these values are considered to be values sampled from thesinusoidal curve, the phase can be obtained as the initial phase byfitting to the sinusoidal curve.

DISCLOSURE OF THE INVENTION

[0009] As mentioned above, both the light section method and theconfocal method also need to perform many image inputs and much imageprocessing for one measurement, therefore high-speed measurement cannotbe hoped for. Moreover, measurement of moving objects is impossible evenwith the comparatively high-speed grating projection phase shiftingmethod since at least three images with a time gap are required.

[0010] An object of the present invention is to realize high-speedsurface form measurement that can deal with moving objects.

[0011] In order to solve the above-mentioned technical problems, thepresent invention proposes a polarization direction detection typetwo-dimensional light reception timing detection device comprising: alinear polarization rotation means to linearly polarize incident lightand to rotate the polarization direction; an analyzing means to dividethe incident light which passes through the linear polarization rotationmeans into at least two different linear polarization components; atleast two synchronized charge type imaging devices that receive eachdivided incident light ray and convert the light intensity into anelectric signal, and output the signal; and an image analysis devicewhich analyzes a plurality of image signals output from the charge typeimaging devices.

[0012] The polarization direction detection type two-dimensional lightreception timing detection device can have more reliability by equippingit with the depolarizing means which converts the incident light tolight with almost no intensity change with respect to the polarizationdirection before the incident light enters the linear polarization lightrotation means. The surface form measurement device by the light sectionmethod comprises an imaging lens; a slit light scanning means toilluminate an object plane of the imaging lens with at least one slitlight from an angle different from the optical axis direction of theimaging lens, and to scan the slit light over the object plane; and thepolarization direction detection type two-dimensional light receptiontiming detection device wherein the charge type imaging devices havebeen arranged at an image plane of the imaging lens; wherein the fieldof view of the charge type imaging devices is scanned by the slit lightscanning means within one exposure time of the charge type imagingdevices, and the polarization direction of the incident light to theanalyzing means is rotated in synchronization with the scanning of theslit light ray by the linear polarization rotation means. Furthermore,the surface form measurement device of the confocal method comprises aconfocal imaging optical system; a Z-direction scanning means whichchanges the relative optical pass length between an object and theconfocal imaging optical system; and the polarization directiondetection type two-dimensional light reception timing detection devicewherein the charge type imaging devices have been arranged at an imagingplane of a confocal imaging optical system; wherein, within one exposuretime of the charge type imaging devices, a measurement range is scannedby the Z-direction scanning means, and the polarization direction ofreflective light from the object incident on the analyzing means isrotated by the linear polarization rotation means in synchronizationwith the scanning over the measurement range.

[0013] Furthermore, the surface form measurement device comprises animaging lens; an illuminating means to illuminate an objectsimultaneously in pulses; and the polarization direction detection typetwo-dimensional light reception timing detection device wherein thecharge type imaging devices have been arranged at the image plane of theimaging lens; wherein, within one exposure timeof the charge typeimaging devices, the whole measurement range is illuminatedsimultaneously at least once by the illuminating means, and the time bywhich the charge type imaging devices have received the object reflectedlight is detected.

[0014] Constituting the surface form measurement device as mentionedabove, measurement is completed by only one exposure time and theprocessing of several images taken simultaneously without a time gap,thus high-speed measurement applicable also to moving objects isattained.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a figure for explaining a first embodiment of thepolarization direction detection type two-dimensional light receptiontiming detection device of the present invention.

[0016]FIG. 2 is a figure for explaining polarization axis directions ofa polarizer and analyzers of the first embodiment of the polarizationdirection detection type two-dimensional light reception timingdetection device.

[0017]FIG. 3 is a figure showing change of the incident light intensityafter the light has passed through the analyzers in the first embodimentof the polarization direction detection type two-dimensional lightreception timing detection device.

[0018]FIG. 4 is a figure showing change of the light intensity ratioafter the light has passed through the analyzers in the first embodimentof the polarization direction detection type two-dimensional lightreception timing detection device.

[0019]FIG. 5 is a figure for explaining a second embodiment of thepolarization direction detection type two-dimensional light receptiontiming detection device of this invention.

[0020]FIG. 6 is a figure for explaining the polarization axis directionsof the polarizer and the analyzers in the second embodiment of thepolarization direction detection type two-dimensional light receptiontiming detection device.

[0021]FIG. 7 is a figure showing change of the incident light intensityafter the light has passed through the analyzers in the secondembodiment of the polarization direction detection type two-dimensionallight reception timing detection device.

[0022]FIG. 8 is a figure for explaining the light section surface formmeasurement system of the present invention.

[0023]FIG. 9 is a figure for explaining the function of the lightsection surface form measurement system of the present invention.

[0024]FIG. 10 is a figure for explaining the confocal surface formmeasurement system of the present invention.

[0025]FIG. 11 is a figure for explaining the conventional light sectionsurface form measurement system.

[0026]FIG. 12 is a figure for explaining the conventional confocalsurface form measurement system.

[0027]FIG. 13 is a figure for explaining the conventional gratingprojection phase shift surface form measurement system.

[0028]FIG. 14 is a figure for explaining the sinusoidal grating used inthe conventional grating projection phase shift surface form measurementsystem.

EXPLANATION OF SYMBOLS

[0029]1 Depolarizing means

[0030]2 Polarizer

[0031]3 Rotation mechanism

[0032]4 Non-polarizing beam splitter

[0033]5 and 6 Analyzer

[0034]7 and 8 Charge type imaging device

[0035]9 Image analysis device

[0036]10 Object

[0037]111 Laser slit light source

[0038]112 Scanning mechanism

[0039]113 Imaging lens

[0040]114 Television camera

[0041]115 Image processing device

[0042]116 Display device

[0043]121 Confocal imaging system

[0044]122 Position in focus

[0045]123 Detector

[0046]124 Z stage

[0047]502,503, and 504 Analyzer

[0048]505,506, and 507 Charge type imaging device

BEST MODE FOR CARRYING OUT THE INVENTION

[0049] Hereafter, with reference to the drawings, the form of theembodiment of this invention will be explained in detail. The firstembodiment of the polarization direction detection type two-dimensionallight reception timing detection device of the present invention isshown in FIG. 1.

[0050] Light propagated from the left-hand side is depolarized by adepolarizing means 1. If the incident light is light with a certainbandwidth, a so called “Lyot” depolarizer suits the depolarizing means1, which is made of two crystals, one of which is a few times thickerthan the other, bonded together in such a way that the angle made by thetwo optical axes is 45 degrees. Or if the incident light is linearlypolarized to a certain angle, a ¼ wave plate and the like may be used.It is necessary to merely provide light which does not change a greatdeal in intensity by the direction of the polarization when the light islinearly polarized. It does not, however, need to be completelydepolarized. For example, it is sufficient also when the light iscircularly polarized, by a ¼ wave plate, as mentioned above. Moreover,there is, in some cases, no need to use a depolarizing means 1, sincethe incident light itself is already in a depolarized state because ofthe character of the light source and an object to be used. Moreover,depending on the kind of linear polarization rotation means explainedbelow, there is no need to depolarize the light.

[0051] Depolarized light (or circularly polarized light) is incident ona linear polarization rotation means which consists of a polarizer 2 andits rotation mechanism 3, and turns into linear polarized light, thedirection of the polarization rotates as time progresses. The linearpolarization rotation means may be realized by elements withelectro-optic effect, magneto-optic effect, or the like so that the axisdirection of the linear polarized light is rotated (optical rotation) astime progresses. For example, since the liquid crystal has opticalrotational power, it can rotate the polarization direction of the linearpolarized light after passing a fixed polarizer electrically. In thiscase, the depolarizing means 1 is unnecessary.

[0052] The incident light which became linearly polarized light with therotating polarization direction reaches an analyzing means whichconsists of a non-polarized beam splitter 4, and two analyzers 5 and 6with their optical axes mutually crossing at a right angle. Regardlessof the direction of polarization using the non-polarizing beam splitter4, the light wave is split into two optical waves with the polarizationstates remaining as before, and the energy becomes half respectively.The components which are perpendicular to each other pass through theindividual analyzers 5 and 6, and the intensity of each component isdetected by two charge type imaging devices 7 and 8.

[0053] As an analyzing means, a polarizing beam splitter which hasfunctions of both the non polarizing beam splitter 4 and analyzers 5 and6 may, of course, be used because of a lower optical loss. In order toraise the accuracy of the polarizing characteristic, not only may thepolarization beam splitter be used, analyzers 5 and 6 may also be used.

[0054] Two charge type imaging devices 7 and 8 are disposed optically inthe same position. For example, when the devices are used with a imaginglens, these are arranged so that the light reception surface of thecharge type imaging devices 7 and 8 may come to the image plane of theimaging lens, and this optical distance (optical pass length) from theimaging lens to the two charge type imaging devices 7 and 8 bothcompletely come to be the same. Moreover the pixels of the samecoordinates (xi, yi) of the charge type imaging devices 7 and 8correspond to the same position on the surface of an object. (This isnot an absolute condition. The condition is eased by having acompensation means. But for the time being, it is assumed that theabove-mentioned condition is fulfilled here.) Moreover, operation ofthese two charge type imaging devices 7 and 8 is synchronized. That is,the release timing of each shutter and the duration of shutter releasingare always in agreement, and the obtained images are simultaneously sentto an image analysis device 9 as electric signals. Inside of the imageanalysis device 9, light reception timing is calculated for every pixelfrom the two sheets of images obtained simultaneously from the chargetype imaging devices 7 and 8 respectively.

[0055] As the charge type imaging device, the most common device atpresent is a two-dimensional CCD camera, but any two-dimensionaldetection device of all pixel simultaneous exposure types isappropriate.

[0056] The above is the structure of the first embodiment of thepolarization direction detection type two-dimensional light receptiontiming detection device. Next, the function of this device is described.This device can record the timing (time difference) at which lightarrives on each pixel within the duration of one exposure of the chargetype imaging devices 7 and 8 by the direction of polarization.

[0057] With reference to FIGS. 2-4, the function is explained in detail.As in FIG. 2, the polarization direction θ after passing the linearpolarization rotation means rotates at an angular velocity ω with theinitial state parallel to the polarizer 5. Supposing a continuous lightof constant intensity is incident on the device, the intensity of theincident light after passing through the two analyzers 5 and 6 willbecome as shown in FIG. 3. Here, when the polarization direction θ isconsidered only between 0-π/2 after passing through the linearpolarization rotation means, the calculation of the ratio of incidentlight intensities (b−a)/(a+b) after passing through the two analyzers 5and 6 will be as shown in FIG. 4, and it becomes almost linear except atboth ends, and more correctly, it changes in a sinusoidal form.

[0058] The case of an incoming pulse-light and not a continuous light isconsidered. Suppose that the polarization direction θ after passingthrough the linear polarization rotation means rotates 0-π/2 and thelight comes only at the time ti. The shutters of the charge type imagingdevices 7 and 8 are released in synchronization with a polarizationdirection rotation. That is, suppose that while the polarizationdirection rotates from 0 to π/2 and the shutters are kept released, theoutput of ai and bi will be obtained according to the polarizationdirection θ when the light reaches the charge type imaging devices 7 and8 respectively, as shown in FIG. 3. From these values, θi can beobtained by calculation of the ratio of intensity (b−a)/(a+b), and bycorrespondence with the FIG. 4. Moreover the time ti is derived byti=θi/ω. If pulse lights reach to each pixel at different timings, andif the timings are within the exposure duration of the charge typeimaging devices 7 and 8, the intensity ratio of each pixel shows thepolarization direction of each timing, thereby the light receptiontiming of light can be calculated for every pixel with the imageanalysis device 9.

[0059] The above is the first embodiment of the polarization directiondetection type two-dimensional light reception timing detection device.Next, a second embodiment of the polarization direction detection typetwo-dimensional light reception timing detection device is explainedusing FIGS. 5-7.

[0060] The second embodiment of the invention of the polarizationdirection detection type two-dimensional light reception timingdetection device is shown in FIG. 5. Since the depolarization means 1and the linear polarization rotation means are completely the same asthose of the first embodiment, their explanation is omitted. An incidentlight that has become linearly polarized light with the rotatingpolarization direction is split by a beam splitter 501 into threedirections. In the first embodiment, the number of division was two, andthe fact that light is divided into three directions differs from thefirst embodiment. Although the explanation given below is for the casewhere the number of divisions is three, the number of directions is notnecessarily restricted to three. More than three directions are alsoacceptable.

[0061] A beam splitter 501 as shown in FIG. 5, as an example, isrealizable by using an amplitude division coatat the bonded portion of acombination prism that is commonly used in a 3 CCD type color camera. Ifthe flux division ratio of the coat near the side of the incident lightis set to 1:2, and another coat is set to 1:1, then division into threebecomes possible. Four right-angled prisms can be used by bonding themtogether. If a coat with half flux division is used on all bondingplanes, light from an arbitrary direction is projected in an individualdirection with the ¼ flux.

[0062] As shown in FIG. 6, incident light divided into three reachesanalyzing means consisting of three analyzers 502, 503, and 504, forwhich the polarization directions differ by π/3, from each other.Regardless of the direction of polarization, the polarization stateremains as is, and its flux is divided into ⅓ to ¼ by a beam splitter501, and the intensity of the light which passes through three sheets ofanalyzers 502, 503, and 504, with the polarization directions differingby π/3, is detected by three charge type imaging devices 505, 506, and507.

[0063] The three charge type imaging devices 505, 506, and 507 arearranged optically at the same position. For example, in the case inwhich these devices are used with a imaging lens, although these arearranged so that the light reception plane of the charge type imagingdevices 505, 506, and 507 comes to the image plane of the imaging lens,this optical distance (optical pass length) from the charge type imagingdevices 505, 506, and 507 to the imaging lens becomes completely thesame, and the pixel of the same coordinates (xi, yi) of the charge typeimaging devices 505, 506, and 507 corresponds to the same position onthe object. (This condition is not absolute and with some compensationmeans could be eased. For the time being, explanation is given on theassumption that the above-mentioned conditions are fulfilled here.)Moreover, operation of these three charge type imaging devices 505, 506,and 507 is synchronized. That is, the release timing of each shutter andthe duration of the shutter releasing are always in agreement, and theobtained images are simultaneously sent to the image analysis device 9as electric signals. Inside the image analysis device 9, light receptiontimings are calculated for every pixel from three images obtainedsimultaneously from the charge type imaging devices 505, 506, and 507,respectively.

[0064] The above is the structure of the second embodiment of thepolarization direction detection type two-dimensional light receptiontiming detection device. Next, the function of this device is described.This device can record the timing (time difference) at which lightarrives on each pixel within one exposure of the charge type imagingdevices 505, 506, and 507, by the directions of polarization.

[0065] With reference to FIGS. 6 and 7, the function will be explainedmore specifically. As shown in FIG. 6, when the polarization direction θafter being subjected to a linear polarization rotation means rotates atan angular-velocity ω, supposing that an initial state is parallel to ananalyzer 502, and a continuous light of constant intensity is incidenton the device, the change of the incident light intensity after passingthrough three analyzers 502, 503, and 505, is sinusoidal wave-like asshown in FIG. 7 with a phase shift of 2π/3 (polarization directionπ/3)mutually.

[0066] Next, the case where the incident light is not continuous but apulse is considered. Suppose that the polarization direction θ afterpassing through the linear polarization direction rotation means rotatescontinuously, and light is incident at an instant ti only. Supposing theshutters of the charge type imaging devices 505, 506, and 507 arereleased at the polarization direction θ=0 and it is exposed until, forexample, θ=Nπ, as shown in FIG. 7, the outputs (ai, bi, and ci) of thecharge type imaging devices 505, 506, and 507 are obtained respectivelyand the outputs (ai, bi, and ci) correspond to the polarizationdirection θi of the timing when the light enters. Therefore θi can becalculated from these values. However, one must note that the calculatedθi contains indefiniteness of nπ. Specifically, if I is the mean lightintensity and I·γ is the grating pattern amplitude, then

[0067] ai=I[1+γ·cos(θi−2π/3)], bi=I[1+γ·cos(θi)], and

[0068] ci=I[1+γ·cos(θi+2π/3)], therefore,

[0069] θi=arctan[{square root}3·(ai−ci)/(2bi−ai−ci)]. Furthermore, thetiming ti can be derived by the operation of ti=θ/ω (nπ/ω isindefinite). Suppose pulse light is incident on each pixel at adifferent timing. If this is within the duration of the exposure of thecharge type imaging devices 505,506, and 507, the pixel output of theintensity ratio that shows the polarization direction θ at the timing oflight reception for every pixel will be obtained, and the lightreception timing can be calculated for every pixel with the imageanalysis device 9.

[0070] Here, although three analyzers 502, 503, and 504 with apolarization direction differing by π/3 were considered, this of coursedoes not limit the present invention. Each interval of a polarizationdirection can be π/4, and may be random. The only requirement is thatthe polarization directions of polarizers are known. There could be morethan three analyzers, four or five are also acceptable. The onlyrequirement is to be able to fit the values to the sinusoidal wave.Using more values leads to higher phase detection accuracy.

[0071] In the first embodiment or in the second embodiment, the reasonwhy this invention is new and effective is that the timing when theincident light hits each pixel can be derived with only one exposure(although a set of images is acquired). Conventionally, when using acharge type imaging device like a CCD camera in order to detect thetiming of incident light on each pixel, many images must be takencontinuously, and the image that gives the maximum pixel output ischosen, and from the number of the image (the order with respect totime), the light incident timing is derived.

[0072] Next, we discuss more specific examples of how the light sectionmethod, the grating projection phase shifting method, and the confocalmethod are made faster using the polarization direction detection typetwo-dimensional light reception timing detection device.

[0073] Using FIG. 8, we first discuss how to make the light sectionmethod faster. The FIG. 8 shows an example of the first embodiment ofthis invention of the polarization direction detection typetwo-dimensional light reception timing detection device applied to aconventional system of the light section method. The principle ofmeasurement of relief on an object 10 is the same with the conventionalsystem. That is, a slit light is projected on the object 10 at an angledifferent from the optical axis of an imaging lens 113 and scanned by ascanning means 112 over the whole field of view determined by theimaging lens 113 and a charge type imaging devices 7 and 8. By detectingthe timing of light incident on each pixel in the charge type imagingdevices 7 and 8 (or of the slit light passing the object 10 surfacepoint corresponding to the pixel), the angle of the slit light isderived from the timing. The position of the surface of the object 10 iscalculated as the crossing point of the two lines; one line is made bythe chief ray of the imaging lens 113 incident to the pixel, and anotherline is made by the slit light with the angle determined as above.

[0074] In the example like this light section method of the slit lightscan type, if we set aside special cases such as multiple reflectionsdue to the gloss of the object 10 surface or having two or morereflective surfaces in the optical axis direction like a film or glassplate, the only time at which a light is incident on a certain pixel iswhen the slit light passes the corresponding point on the objectsurface, and that is only once in a scanning over one field of view.

[0075] If, while the shutters (electronic shutter) of the charge typeimaging devices 7 and 8 are kept released, the direction of the linearpolarization light incident to the analyzers can be rotated insynchronization with the slit light scanning over the whole field ofview from the left end to the right end of FIG. 8 (for example, when theslit light is at the right end, the polarization direction is 0, andwhen the slit light is at the left end, the polarization direction isπ/2, and between them, it rotates at a constant angular velocity ω),lights like pulse are incident on each pixel only when the slit lightpasses the corresponding surface position of the object 10 and when thescanning of the slit light is completed and the shutter of the chargetype imaging devices 7 and 8 are shut, the intensity ratio which showsthe polarization direction when the incident light hits the pixel willbe recorded at each pair of pixels of the charge type imaging devices 7and 8.

[0076]FIG. 9 shows the state in which, at the timing tp, the light hitsa pair of pixels P′ and P″ in the charge type imaging devices 7 and 8(when the slit light passes the corresponding point on the surface of anobject) in FIG. 8, in which the horizontal axis indicates thepolarization direction. Since lights are incident on the charge typeimaging devices 7 and 8 only at the timing of tp, output values can beobtained which are proportional to the light intensity ai and bi,corresponding to the polarization direction θi at the time. θi isderived from the intensity ratio (bi−ai)/(ai+bi), and the timing can becalculated by the formula ti=θi/ω.

[0077] If light reception timing of all pixels is obtained as mentionedabove, the height (Z position) of the object 10 surface corresponding toeach pixel can be calculated by easy processing of the image analysisdevice 9, since the following information can be obtained in advance:the relation of the timing and the projection angle of the slit light,the chief ray angle of the imaging lens 113 as that ray hits each pixel,and the geometrical arrangement between the imaging lens 113 and thescanning mechanism 112.

[0078] If all the combinations of ai and bi for every pixel arecalculated and stored in a table in advance, the output value of thecharge type imaging devices 7 and 8 can also be changed directly intothe surface height of the object 10 by merely using the table. Ofcourse, it is also possible to constitute a reference table with thevalues of the intensity ratio (bi−ai)/(ai+bi). At any rate, sincecalculation of the surface form of an object 10 is very simple, even bysoftware processing, sufficient video rate measurement of the surfaceform of an object 10 can be realized by using a high-speed CPU.

[0079] The implementability of hardware parts of the system is nowexamined briefly. Suppose a Galvano scanner is used as a scanningmechanism 112, less than 1 ms of the scan over one field of view ispossible and one quarter rotation (0−π/2 polarization directionrotation) within 1 ms (15000 rpm) is easily performed if a motor is usedas a polarization rotation means. That is, not only measurement of thevideo rate (33 ms) is possible, but three-dimensional freezingmeasurement (which correspond to high-speed shutter operation of acamera) of moving objects is also possible.

[0080] Next, measurement resolution ability is considered. Themeasurement resolution ability is obviously restricted by the angledetection resolution ability of a projection slit. The number ofdivisions within the scanning angle range is important, but as is clearfrom FIG. 3, since the device can be only used in the domain of themonotone increasing or decreasing, the number of divisions can notnormally exceed the quantization number (gradation number) S of a image,which number is detection values of the detector that varies from 0 toS. In fact, it will become much smaller than S due to heterogeneity ofreflectance of the object or the noise factor due to various causes.

[0081] The case that the second embodiment is applied to the system asthe polarization direction detection type two-dimensional lightreception timing detection device is considered hereafter. In the caseof the second embodiment as shown in FIG. 7, the domain is notrestricted in the monotone increasing or decreasing region, at least therange from 0 to π can be used, and if the indefiniteness of nπ ispermitted, the domain over more than two cycles can be used, thus a veryfine angle detection resolution can be provided. For example, supposingN cycle domain is used, a slit will be scanned from one end of a imageto the other within one exposure time of the charge type imaging devices505, 506, and 507, and the polarizer 2 will rotate N/2 times. In thisway, sinusoidal grating pattern images with N fringes are obtained andthe phase of grating of each three images has shifted mutually. That is,if one takes only the obtained images into account, images completelythe same as the ones obtained from the grating projection phase shiftingmethod are obtained. If processing equivalent to that used in thegrating projection phase shifting method is applied, measurement of thesame accuracy as the grating projection phase shifting method cannaturally be performed. All are not the same necessarily. Projectedpatterns may not be sinusoidal patterns which are difficult tomanufacture, a rectangle-slit is sufficient. Since three phase shiftimages can be obtained simultaneously, a good characteristic isprovided, in that the measurement for moving objects is possible.Moreover, the number of slits does not need to be one. For example, if Nslits are provided, the scanning range becomes 1/N and light intensityis quantitatively advantageous. When two or more slit lights areprojected, the direction of polarization must be made to become the sameat the beginning of a scan as at the end of the scan, that is, thedirection is a multiple of π.

[0082] Next, improvement in the speed of the confocal method isexplained using FIG. 10. In the conventional device using the confocalmethod in FIG. 12, the polarization direction detection typetwo-dimensional light reception timing detection device of the firstembodiment is used instead of the usual detector 123. As stated above,the confocal imaging system 121 has the feature where only light from aportion in focus arrives at the charge type imaging devices 7 and 8 asreflective light of an object 10, while hardly any light from a portionout of focus reaches the charge type imaging devices 7 and 8. Therefore,as the object 10 is scanned in the direction of the optical axis withthe Z table 124, light reaches the pixel only when the surface of theobject 10 passes the conjugate position (the three dimensional imagingposition of the pixel in the object side of the objective lens) of eachpixel of the charge type imaging devices 7 and 8, and at other timing,light will not reach the pixel. The timing at the light reception willexpress the position of the Z table 124 at that time, and the positionwill show the relative position of the surface of an object 10 in theoptical axis direction.

[0083] Although calculation methods to convert the light receptiontiming to the surface height of the object 10 differ completely, lighthits each pixel of the charge type imaging devices 7 and 8 just once ina pulse. Therefore the surface position is derived from the timing, andit is completely the same as that of the example of the light sectionmethod mentioned above.

[0084] While the shutters of the charge type imaging devices 7 and 8 arereleased in synchronization with scanning of the Z table 124 over thewhole measurement range (from top to bottom in FIG. 10), if thedirection of linear polarization incident to the analyzing means isrotated by linear polarization rotation means (for example, thedirection of polarization is zero at the top end of the Z table, and π/2at the bottom, in between, it rotates with a constant angular velocityω), at each pixel, light enters as a pulse only when the surface of theobject 10 passes the conjugate position and when a scan of the Z table124 is completed and the shutters of the charge type imaging devices 7and 8 are shut, the intensity ratio which shows the polarizationdirection at the time of light hitting each pair of pixels of the chargetype imaging devices 7 and 8 will be recorded. All that is necessary isto convert back to the surface height of the object 10 on the imageanalysis device 9.

[0085] Also in the confocal method, in order to raise measurementresolution ability, the second embodiment of the polarization directiondetection type two-dimensional light reception timing detection devicecan be introduced. All that is necessary is to rotate the polarizer 2 asmany times as possible during one exposure/scan, and derive the position(namely, object surface position) at which light is reflected, as aninitial phase from the three images with different phases. However,since the indefiniteness of nπ exists, phase connection processing isneeded.

[0086] Next, the time of flight method (hereinafter referred to as “TOFmethod”) similarly known as the surface form measurement technique isconsidered. The TOF method is also realizable by the polarizationdirection detection type two-dimensional light reception timingdetection device. The TOF method is a technique of measuring the reliefon the surface of an object by measuring the time interval from lightemission until it is reflected by the object and returned. Since thisinvention is a technique for measuring time, this invention isapplicable. That is, pulse-light is irradiated simultaneously at thewhole object and returning light is received at the polarizationdirection detection type two-dimensional light reception timingdetection device through an imaging lens. Since the time after the lightis emitted and returned differs according to the object surface'srelief, the time difference can be measured with the polarizationdirection detection type two-dimensional light reception timingdetection device, and thereby, an object surface form can be determined.

[0087] Although examples of the polarization direction detection typetwo-dimensional light reception timing detection device applied tosurface form measurement were shown, the scope of the polarizationdirection detection type two-dimensional light reception timingdetection device is not limited only to these cases. The invention canapply to phenomenon where two-dimensional position is important and ateach position, light is radiated or reflected/penetrated only as apulse. For example, applications to locus measurement of a high-speedmoving object, visible light communications, or the like can also beconsidered.

Industrial Applicability

[0088] By this invention, with only one time of imaging (one exposure),one can detect light reception timing for every pixel, and more thanseveral to a few hundred times faster measurement of the surface formmeasurement is possible than with the conventional methods concernedwith the light section method, the grating projection phase shiftingmethod, the confocal method, and the TOF method. Since measurement ofmoving objects becomes possible, a large effect in extensive fields,such as three dimensional high-speed phenomenon analysis, thethree-dimensional vision for a robot or a car, the three dimensionalmeasurement of living bodies of animals and plants, security, and FA isexpected.

1 A polarization direction detection type two-dimensional lightreception timing detection device, comprising: a linear polarizationrotation means to linearly polarize incident light and to rotate thepolarization direction; an analyzing means to divide the incident lightwhich passes through the linear polarization rotation means into atleast two different linear polarization components; at least twosynchronized charge type imaging devices that receive each dividedincident light ray and convert the light intensity into an electricsignal, and output the electric signal; and an image analysis devicewhich analyzes a plurality of image signals output from the charge typeimaging devices. 2 The polarization direction detection typetwo-dimensional light reception timing detection device according toclaim 1, comprising a depolarizing means to convert the incident lightto light with small intensity variation with respect to polarizationdirections before the light enters the linear polarization rotationmeans. 3 A surface form measurement device, comprising: an imaging lens;a slit light scanning means to illuminate an object plane of the imaginglens with at least one slit light from an angle different from theoptical axis direction of the imaging lens, and to scan the slit lightover the object plane; and the polarization direction detection typetwo-dimensional light reception timing detection device according toclaim 1 wherein the charge type imaging devices have been arranged at animage plane of the imaging lens; wherein the measurement range of thecharge type imaging devices is scanned by the slit light scanning meanswithin one exposure time of the charge type imaging devices, and thepolarization direction of the incident light to the analyzing means isrotated in synchronization with the scanning of the slit light by thelinear polarization rotation means. 4 A surface form measurement device,comprising: a confocal imaging optical system; a Z-direction scanningmeans that changes the relative optical pass length between an objectand the confocal imaging optical system; and the polarization directiondetection type two-dimensional light reception timing detection deviceaccording to claim 1 wherein the charge type imaging devices have beenarranged at an image plane of a confocal imaging optical system;wherein, within one exposure time of the charge type imaging devices, ameasurement range is scanned by the Z-direction scanning means, and thepolarization direction of reflective light from the object incident onthe analyzing means is rotated by the linear polarization rotation meansin synchronization with the scanning over the measurement range. 5 Asurface form measuring device, comprising: an imaging lens; anilluminating means to illuminate an object simultaneously in pulses; andthe polarization direction detection type two-dimensional lightreception timing detection device according to claim 1 wherein thecharge type imaging devices have been arranged at the imaging plane ofthe imaging lens; wherein, within one exposure time of the charge typeimaging devices, the whole measurement range is illuminatedsimultaneously at least once by the illuminating means, and the time bywhich the charge type imaging devices have received the object reflectedlight is detected. 6 A surface form measurement device, comprising: animaging lens; a slit light scanning means to illuminate an object planeof the imaging lens with at least one slit light from an angle differentfrom the optical axis direction of the imaging lens, and to scan theslit light over the object plane; and the polarization directiondetection type two-dimensional light reception timing detection deviceaccording to claim 2 wherein the charge type imaging devices have beenarranged at an image plane of the imaging lens; wherein the measurementrange of the charge type imaging devices is scanned by the slit lightscanning means within one exposure time of the charge type imagingdevices, and the polarization direction of the incident light to theanalyzing means is rotated in synchronization with the scanning of theslit light by the linear polarization rotation means. 7 A surface formmeasurement device, comprising: a confocal imaging optical system; aZ-direction scanning means that changes the relative optical pass lengthbetween an object and the confocal imaging optical system; and thepolarization direction detection type two-dimensional light receptiontiming detection device according to claim 2 wherein the charge typeimaging devices have been arranged at an image plane of a confocalimaging optical system; wherein, within one exposure time of the chargetype imaging devices, a measurement range is scanned by the Z-directionscanning means, and the polarization direction of reflective light fromthe object incident on the analyzing means is rotated by the linearpolarization rotation means in synchronization with the scanning overthe measurement range. 8 A surface form measuring device, comprising: animaging lens; an illuminating means to illuminate an objectsimultaneously in pulses; and the polarization direction detection typetwo-dimensional light reception timing detection device according toclaim 2 wherein the charge type imaging devices have been arranged atthe imaging plane of the imaging lens; wherein, within one exposure timeof the charge type imaging devices, the whole measurement range isilluminated simultaneously at least once by the illuminating means, andthe time by which the charge type imaging devices have received theobject reflected light is detected.